This invention relates to food processors, and more particularly to power lock tool retention apparatus for mounting and holding a rotary tool on a vertical motor-driven shaft for preventing the tool from dynamically lifting or "riding upwardly" along this shaft during-operation of the food processor.
In food processors there is a motor-driven shaft extending upward within a working bowl, and various selected rotary tools can be engaged on this shaft to be driven by the shaft for performing various food processing operations as may be desired by the user. The various rotatable tools, for example those for cutting, chopping and mincing or those for mixing and kneading have different types of blades in accordance with the food processing operation to be performed. Each tool has at least one blade screwed to a hub containing a socket and extending outwardly from the hub. When installing such a blade tool onto the shaft, the user slides the hub vertically down onto the shaft. In order to provide a driving connection between shaft and hub, the shaft is provided with at least one axially extending drive coupling means, such as a flat face. The hub socket has complementary coupling and such as at least one internal axially extending land for engaging the driving coupling means associated with the rotatable drive shaft.
Such rotary blade tools for example, have at least one blade extending outwardly from the hub, positioned relatively low down on the hub so that when the hub is mounted on the drive shaft, the blade is nearer to the bottom than to the top of the working bowl. The result is that during food processing the rapid rotation of the blade relative to the mass of the food being processed often creates a dynamic lifting action on the blade, thereby causing the tool to lift or to ride up or climb along the shaft. The clearance between the lower revolving blade and the bowl bottom progressively increases, until the blade is skimming or skipping over the upper surface of the ass of food material. This dynamic lifting of the tool can have three undesirable results. The elevated tool may not properly or fully process the food in the bowl. If the tool continues to elevate, the tool may be thrown from the upper end of the drive shaft. Or, the tool may chatter on the upper end of the drive shaft, causing undue wear.
A number of approaches have been tried in the prior art in attempts to solve this dynamic lifting problem, none of which has been completely satisfactory. For example, the upper end of the drive shaft can be screw-threaded to use a fastener or suitable nut for securing the hub to the shaft. This practice is time-consuming for the user and is unsanitary, because the food particles can be lodged in the crevices of the exposed screw thread on the upper end of the shaft.
In U.S. Pat. No. 3,493,022 Mantelet, the blade-carrying hub is connected to the drive shaft by helical splines on the lateral surface of the drive shaft engaging with corresponding shaped clearance grooves in the inner surface of the hub bore in which the pitch of the splines and grooves are selected such that one rotation of the drive shaft in its normal direction of rotation fully engages the splines in the grooves. However, in later U.S. Pat. No. 3,970,258 to the same inventor, it is disclosed that the helically grooved tool in certain cases may continue to turn through the effect of inertia when the motor is abruptly stopped and then escapes from the driving shaft, with the consequent risk of causing damage. This second Mantelet patent discloses a shaft with at least one helical driving ramp and in addition at least one helical retaining ramp, which has an active surface facing downwardly and which winds from bottom to the top in the opposite direction to the direction of rotation of the drive shaft. In a complementary manner the hub bore has at least one helical driving ramp and also at least one helical retaining ramp which finds from bottom to top in the opposite direction to the direction of rotation of the driving element and has an active surface facing upwardly. Accordingly, if the tool continues to turn after the driving motor has stopped, the hub retaining ramp will be spontaneously engaged under the retaining ramp on the drive shaft to secure the hub against escape in the upward direction. This dual ramp arrangement is complex requiring multiple ramps on both the interior surface of the hub as well as the exterior surface of the drive shaft. Furthermore, the operator may have to dislodge the complementary ramps to remove the tool which may be difficult if food particles squeeze into the ramp clearances and cause the tool to stick on the shaft.
In U.S. Pat. No. 4,127,342 - Coggiola a snap-on fastener arrangement is provided for preventing the tool from rising along the drive shaft during operation. This snap-on arrangement requires a plurality of detachable resilient retainer clips having hookable surfaces. Such resilient fastening arrangements require a forceful push by the user to achieve full engagement and have a tendency to break or become dislodged, and after periods of wear may not clip properly.